Butadiene-1,3 has been polymerized to form high cis1,4-polybutadiene employing organonickel-based catalyst systems and as cocatalyst systems aluminum alkyl compounds and hydrogen fluoride or a hydrogen fluoride complex.
For instance, in the U.S. Pat. No. 3,856,764 issued Dec. 24, 1974, there is disclosed a process for producing high cis-1,4-polybutadiene which comprises contacting 1,3-butadiene with a catalyst consisting of (1) at least one organoaluminum compound, (2) at least one nickel compound selected from the class consisting of nickel salts of carboxylic acids, organic complex compounds of nickel and nickel tetracarbonyl, and (3) at least one hydrogen fluoride complex prepared by complexing hydrogen fluoride with one or more members of a class consisting of ketones, esters, ethers, alcohols, nitriles and water.
In U.S. Pat. No. 3,910,869 issued Oct. 7, 1975, there is disclosed another process for the polymerization of 1,3-butadiene to form polymers containing a high proportion of the butadiene units in the cis-1,4-configuration. This process comprises 1,3-butadiene under solution polymerization conditions with a catalyst comprising (1) an organoaluminum compound, (2) an organ nickel compound and (3) hydrogen fluoride.
In the process of all of the aforementioned patents 1,3-butadiene is polymerized to a high cis-1,4-configuration polybutadiene of fairly high molecular weight in the neighborhood of 3.0 or greater than 3 DSV (dilute solution viscosity).
There are other United States patents which might be mentioned as producing a high cis 1,4-polybutadiene, such as U.S. Pat. No. 3,170,907 issued Feb, 23, 1965.
There are other patents which utilize aluminum alkyls organonickel compounds and fluorine containing compounds to produce polybutadienes having various molecular weights and physical properties. See U.S. Pat. No. 3,725,492 issued Apr. 3, 1969.
In many applications of which cis-1,4-polybutadiene can be employed, it is usually desirable to employ a lower molecular weight polymer than those generally obtained from either one of the immediately aforementioned polymerization systems. For example, in the manufacture of tires, particularly automobile tires, it is usually desired to use a high cis-1,4-polybutadiene having a DSV of about 3 or slightly higher. On the other hand, if one desires to use the high cis-1,4-polybutadiene as a sealant or in a paint or some other application other than tires it is usually desirable to have a polybutadiene with a DSV of something less than 3, even to a liquid.
The process of the invention described herein deals with the use of various hydrocarbon compounds to regulate the molecular weight of the above-mentioned polymerization systems. The utilization of these molecular weight regulators expands the scope of the organoaluminum/organonickel/fluorine catalyzed 1,3-butadiene polymerization systems in a manner that the molecular weight of the cis-1,4-polybutadiene can be controlled from an extremely high molecular weight elastomer all the way down to a liquid polymer.
In the prior art there are syntheses of various molecular weight polybutadienes which can be produced by an anionic or an emulsion polymerization system by controlling the mechanism of the catalyst, the catalyst level or the chain transfer level, respectively. However, these polymerization systems do not necessarily yield a high cis-1,4-polybutadiene typical of the aluminum/nickel/fluorine-base solution polymerization systems mentioned above. As an example, in a typical alkyllithium initiated system, which is anionic in nature, the 1,3-butadiene is polymerized generally yielding about 36 to 45 weight percent cis-1,4-polymer, about 48 to 50 percent trans-1,4-polymer and about 8 to 10 percent of the 1,2-structure. Butadiene 1-3 has been polymerized in typical emulsion polymerization systems. These emulsion polymerization systems usually result in the polybutadiene having about 60 percent of the product in the trans-1,4-configuration, about 20 percent in the cis-1,4-structure and about 20 percent in the 1,2-structure.
Very low molecular weight polybutadienes have been synthesized using nickel compounds and aluminum halide compounds in solution polymerization systems. However, these catalyst systems do not yield a very high cis1,4 -structure in the polybutadiene which is typical of the nickel carboxylate/organoaluminum/fluorine containing systems. They furthermore do not have the flexibility to yield high molecular weight polymers.
The uniqueness of the present invention is that it expands the scope of the high cis-1,4directing 1,3-butadiene polymerization systems such that they can be employed for the synthesis of the polymers ranging from an elastomer useful in the production of automobile tires to an oily liquid useful in coatings and in other less demanding applications.
The effect of certain hydrocarbon compounds on the polymer intrinsic viscosity (.eta.) in 1,3-butadiene polymerization systems employing nickel-based catalyst systems was studied by Sakata et al, and reported in Die Makromolekulare Chemie, 139 (1970), pages 73-81. In these studies the authors employed a triethylaluminum/ nickel carboxylate/boron trifluoride etherate catalyst system in benzene solvent. The hydrocarbons screened in this study included saturated hydrocarbons, such as propane, n-butane and isobutane. Alpha olefins, such as propylene, butene-1 and isobutene were studied, as well as internal olefins, such as cis and trans butene-2. Concerted diolefins, such as allene and 1,2-butadiene were tried as hydrocarbons to reduce the molecular weight. Further aoetylenes such as methylacetylene, and vinylaoetylene, and nonconjugated diolefins, such as 4-vinylcyclohexene-1 were attempted to be used as molecular weight regulators. The authors of this aper concluded that saturated hydrocarbons and mono-olefins, such as alpha olefins and internal olefins show no effect on the polymer viscosity nor on the conversion. Further, they found that 4-vinylcyclohexene has the effect of lowering the polymer viscosity, however, in order to do so required such amounts as to preclude its employment as a useful molecular weight regulator. The aoetylenes did not lower the molecular weight but they did have a very dramatic detrimental effect on polymer yields.